A torque-shear (TS)-type high strength bolt generally used in a bolt joint for a steel frame structure is regulated in the standard specifications for building construction, and is subjected to axial load introduction (fastening) and axial load test under torque management rules based on the standard.
It has been known that a proper axial load is introduced if a pintail of the torque-shear-type high strength bolt fastened by the torque management rules is fractured. Therefore, the axial load of the torque-shear-type strength bolt has been estimated and predicted by testing an actually introduced fastening axial load based on correlation between a torque coefficient and torque through an axial load tester in a conventional site.
However, the torque coefficient is varied depending on many external factors, such as a stored state of the bolt, nonuse of a provisional bolt, exposure to air and water penetration due to outstanding fastening of the day, attachment of foreign matter, product damage, etc.
Therefore, the actually introduced axial load is significantly different from an estimated value. Thus, there arise problems that the actually introduced axial load is not only inexactly determined but also frequently falls short of the design standard.
Also, there arises a problem that the high strength bolt falling short of the design standard is difficult to replace or be additionally fastened due to difficulty in measurement of the axial load immediately after fastening on site.
To secure the proof stress of the high strength bolt joint for the steel frame structure, it is necessary to introduce a stable axial load variable within a narrow range into the bolt. Accordingly, there is a need for solving the problem that the actually introduced axial load is significantly varied depending on change in the torque coefficient due to the foregoing external environmental factors.
Also, there is a need for immediately measuring the axial load of the high strength bolt after fastening in order to improve quality management regarding the fastening axial load.